Pressurized water delivery pipeline systems and other underground pressurized and unpressurized fluid transport pipes can be difficult to inspect due to their hidden location and the substantial costs related with ground excavation. Leaks in such pipes can increase costs associated with operating the pipe due to disruptions and damages, create potential hazards, and increase public health risks. Additionally water (and often other pipeline fluids) is an important natural resource and water pipelines are crucial in the continuation of our daily lives. Thus, it is beneficial to identify defects in the pipe accurately and quickly, while avoiding disruption to the community's water network services.
Pressurized pipes can be difficult to inspect due to accessibility being limited, difficult, and sometimes dangerous. Therefore, inspection of pressurized pipes with the utilization of a single inspection device is generally beneficial.
One form of defect detection is described in detail in ASTM Standard F2550-13 which describes a low voltage conductivity method for defect detection by measuring variations in electric current flow through walls of the pipe as part of a series circuit including a voltage source and an electric current sensor, which collects data as the probe moves through a known position within the pipe.
One such probe beneficial for use in conducting this low voltage conductivity is provided by Electro Scan, Inc. of Sacramento, Calif. Such probes effectively concentrate the electric current over a relatively short length of the pipe in which the probe is located, so that electric current intensity data gathered by the low voltage conductivity method can be accurately correlated with the condition of the pipe directly adjacent the probe. Additionally, if a water main is lined with a cured-in-place method, low voltage conductivity is able to identify defects that typically go unnoticed by other methods such as cameras and acoustic hydrophones.
However, the low voltage conductivity method is unable to accurately detect leaks in metallic pipes since those pipes conduct electricity, resulting in no significant difference in electric current intensity between the pipe wall and a defect. As a result, when there are sections of metallic pipe within a pressurized system, it may result in data readings which are difficult to decipher.
Another form of defect detection is acoustic hydrophones, which locate defects by listening for the leak noise(s) that travels through the water and pipe walls and records the data. Hydrophones work well in metallic and concrete pipes, but in plastic and asbestos cement pipes the sound does not carry well enough to give an accurate reading. This is due to the sounds resulting from a leak being reduced by the walls of the pipe, which can make them difficult to detect, especially if a hydrophone is too far from a defective wall. Additionally, hydrophones can have the possibility of missing leaks, thereby placing anomalies in the data due to sound interference from occurrences such as surface noise as well as acoustic damping because of the surrounding soil.
A third form of leak detection in pressurized pipes is by utilizing cameras, such as closed-circuit television (CCTV). Cameras aid in the identification of structural defects and air pockets, mapping of service tap and valve locations, investigation of water quality, and so on. However, the identification of defects which leak can be very difficult and easily missed since the camera cannot always see where water is exfiltrating and many defects may be too small or too difficult to locate visually. Asbestos cement pipes or pipes which have been lined using a cured-in-place process further exacerbate these issues. Additionally, minerals that commonly deposit on the walls of the pipe may obstruct the view of a leaking defect.
A fourth form of leak detection in pressurized pipes is by using pressure sensors. Since water pipelines are pressurized, leakage in a pipeline can alter the pressure and flow field of the working medium. Therefore, a fluidic region in the neighborhood of a leak will be created from the rapid change in static pressure, i.e. dropping from high-pressure inside the pipeline to low pressure in the surrounding medium resting outside. This pressure gradient can appear in pressurized pipes in the vicinity of leaks and openings. However, as the pressure in the pipe increases, the smaller leaks become exceedingly difficult to detect.
Each of the aforementioned technologies used in leak detection of pipes have different strengths and weaknesses and thus leave the possibility of falsely identifying leaks and/or completely failing to identify a leak. Hence, it is beneficial to utilize a system which incorporates multiple (or all) of these technologies. Doing so allows for the collection of a wider range of data and information regarding the pipe during a single inspection which not only limits the amount of entrances into the pipe to inspect, but also aids in eliminating false positives, thereby more accurately and safely determining the condition of the pipe.